Over the last two decades, the intensity of twisters pummeling the United States has crept up, geographer James Elsner of Florida State University in Tallahassee reported at the American Geophysical Union’s fall meeting on December 10.

The National Weather Service ranks tornado intensity using the Enhanced Fujita Scale. The EF Scale lumps the storms into one of six categories based on damage to trees, light poles, buildings and other structures. Scientists assign a rating by looking at photographs of a tornado’s aftermath.

But fitting tornadoes into narrow categories gives scientists only a rough gauge of a tornado’s strength. “We need a continuous estimate of tornado intensity,” Elsner argued.

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